The goals of this project are to characterize lymphocyte Fc receptors genetically and functionally. Recent findings indicate that the Fc IgG receptors of B lymphocytes interact with: a) the lymphocyte cytoskeleton, b) Ia antigens and Lym antigens, c) surface IgM, and d) surface IgD. Each of these interactions is distinct, specific, and non-random. These findings strongly suggest that B lymphocyte Fc IgG receptors are central to B lymphocyte activation and immunoregulation.